I just applied to an ACX grant (asking between $ 20k and 50k) to carry out this project https://mariopasquato.substack.com/p/testing-universal-free-fall-with
Scott says that grantees will have "money in their hands" by March 1, 2024. If I do receive at least 10k by March 15, I will resolve YES. Otherwise I will resolve NO. This applies only to money actually wired to my account, not to formal acceptance of the grant. Any delays due to banking issues or other unexpected events do not matter as long as Manifund or suitable related entities actually sent the wire.
This is the text from my application:
The universality of free fall (all materials fall with the same acceleration) is a cornerstone of modern physics. If it were disproved, general relativity would be proven wrong. The history of empirical tests of the universality of free fall is as long as the history of physics, with Galileo already allegedly conducting experiments of this kind. Current experiments test the universality of free fall with great precision (one part in 10^15) on test bodies that typically are spheres of suitable metals (e.g. titanium and platinum in the MICROSCOPE experiment). This does not rule out violations occurring to different materials. Newton seems to have been the last to test a broad array of materials, albeit with a crude method. Modern experiments rely on atomic theory, assuming that at the core all matter is neutrons, protons and electrons. But what if some obscure compound experiences a configuration-dependent fifth force leading to a violation while its constituent atoms or subatomic particles would not? This is very unlikely (how unlikely? Maybe Manifold can tell) but setting probabilities to zero is a display of arrogance. In physics experience should always have the last word. Huge returns are possible if a groundbreaking discovery happens this way; otherwise we can just fell more confident that free fall is universal, which is still a result.
The goal of this project is to empirically test the universality of free fall with a citizen science setup. Essentially I will arrange to manufacture experimental kits resembling the original setup by Newton with two pendulums whose bobs are identical and can be filled with different compounds in the same amount (as measured in terms of gravitational mass by weighing) and to distribute those kits to citizen-scientists, probably high schools, libraries or groups of interested citizens. The goal is to provide them with an ikea-like experience, so they can easily assemble the kit and take the relevant measurements. This amounts to measuring the period difference between the two pendulums and should be precise to few parts in 1000.
The kits would be useful for demonstration purposes anyway in a physics lab, but unlike your ordinary demonstration they would let the participants contribute to actual science: I plan to publish an academic paper on the results once the data collection is completed, and the paper would acknowledge the participants by name. In fact the kits could even be sold or given in exchange of a small donation, allowing the project to recoup at least a fraction of the costs.
Edit, addendum: Would this grant have good scientific returns in expectation?
At present we are between 3% and ~0.5% probability that a violation is detected in my experiment (see linked markets) and at around 30% probability that I find a not completely trivial explanation for the violation. All told >0.1% probability of getting something cool (a shot at new physics) out of this grant. If you estimate the value of having a good chance of discovering new physics at about the price of a big science experiment (~10^7-10^9 $) then this is pretty good value for the grant money (in expectation). See https://open.substack.com/pub/mariopasquato/p/costs-probabilities-expectations and https://mariopasquato.substack.com/p/compounds-compounds for further discussion.
Related questions
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https://open.substack.com/pub/astralcodexten/p/acx-grants-results-2024
Basically the answer is no, but leaving this up for now because the wording of the question does not consider “formal acceptance”. Is anyone opposed to me resolving NO early?
@EstMtz Last year there were 656 applicants of which I counted 38 that were funded. So the base rate should be about 6% or a bit less if you count only those grantees who got more than 10k$. See https://www.astralcodexten.com/p/acx-grants-results
@EstMtz Yes I have a list of about 70 compounds selected based on the following principles: 0 or 1 rating as a health hazard in their fire diamond (for comparison sodium chloride is 1, so this is very harmless stuff); easy availability for a reasonable price; good shelf stability; coverage of a large number of constituent elements, chemical bond type, crystal structure (if applicable); simplicity (I prefer including simple salts over big organic molecules with some exceptions). Three extracted at random from the list: dimagnesium phosphate, bismuth III oxide, zinc sulphide.
I plan to put up a tentative list on my blog with data for each compound such as fraction by mass of each element, nuclear properties of the constituent elements (mass defect, etc.).
@mariopasquato
From ChatGPT:
In testing the Weak Equivalence Principle (WEP) using pendulum experiments with a wide range of substances, the goal is to examine how different materials respond to gravity and whether there are any variations in the acceleration of free fall. The importance of testing various types of compounds lies in the desire to explore the fundamental nature of mass and gravity across different atomic compositions and structures. Here are some types of compounds that might be considered important for such tests:
Diverse Elements:
Testing elements from different parts of the periodic table is crucial. This includes metals, nonmetals, and metalloids. Comparing the behavior of, for example, a metal pendulum with a nonmetal pendulum can provide insights into how the composition affects the response to gravity.
Composite Materials:
Testing materials composed of mixtures of elements can be valuable. Composite materials are prevalent in various applications, and their response to gravity might differ from that of individual elements.
Organic Compounds:
Organic compounds, which contain carbon and hydrogen, are important to test. This category includes a wide range of substances, from simple hydrocarbons to complex organic molecules. Understanding how organic compounds behave under the influence of gravity is relevant to biological and chemical applications.
Minerals and Crystals:
Testing minerals and crystals can provide insights into the gravitational behavior of structured materials. Different crystal structures may exhibit unique responses to gravity.
Polymers:
Polymers, which are large molecules composed of repeating structural units, are commonly used in materials and everyday products. Investigating how polymers respond to gravity can have implications for the design and understanding of materials.
Fluids and Gases:
Testing fluids and gases is also important, as their response to gravity can differ from that of solids. This category includes liquids, such as water and various solutions, as well as gases like air.
Exotic Materials:
Exploring the behavior of exotic materials, such as superconductors or materials with unique electronic or magnetic properties, can be intriguing. These materials may exhibit unconventional responses to gravity.
Materials with Unusual Properties:
Materials with unique properties, such as those that exhibit negative refractive index or other exotic characteristics, could be of interest. Testing such materials can provide insights into the interplay between material properties and gravity.
Biological Materials:
Testing biological materials, including tissues and biomolecules, can be relevant. Understanding how living organisms respond to gravity is important for biological research and potential applications in space exploration.
Synthetic Materials:
Testing materials designed for specific applications, including those developed for technological or industrial purposes, is also valuable. These materials may have tailored properties that influence their gravitational behavior.
@mariopasquato chatGPT knew, but was entertaining the idea
"As of my last knowledge update in January 2022, there have been no experimental observations indicating a deviation from the Weak Equivalence Principle (WEP) or the broader equivalence principle in the realm of classical gravity. Experiments testing the equivalence principle, particularly the WEP, have been conducted with high precision, and the results have consistently supported the principle within the limits of experimental accuracy.
The most stringent tests of the equivalence principle have been carried out in various contexts, including lunar laser ranging experiments, satellite-based experiments, and laboratory experiments involving different materials and substances. These experiments have not revealed any significant violations of the equivalence principle.
It's important to note that experimentalists in the field of gravity and fundamental physics are continuously refining their methods, increasing the precision of measurements, and exploring new avenues for testing gravitational principles. Any experimental observation deviating from the equivalence principle would be groundbreaking and would likely prompt further investigations and potentially lead to modifications or extensions of our current understanding of gravity."
@EstMtz There is now a google doc linked here with a list of compounds, linear formulae, health hazard ratings, and prices: https://mariopasquato.substack.com/p/compounds-compounds
@mariopasquato looks good so far. nice write up and selection of compounds, I'll volunteer to test elemental mercury if this gets funded haha.
@EstMtz Ahah it’s liquid and conductive (and toxic but ok, as a kid I would play with mercury droplets from a broken thermometer and I am still alive) so it’s going to be a pain to measure. Any coupling between the motion of the bob wrt the wire and the internal motions of a liquid will dissipate energy, reducing the amplitude faster, which leads to a different period due to anharmonic corrections (the pendulum is not an ideal oscillator). Conductivity may lead to dissipation also because of the Earth’s magnetic field. In fact there’s a bunch of other “easy” elements with solid compounds I did not include yet like strontium (the naturally occurring isotope is not radioactive and there are several compounds with a rating of 1) or cerium.
@mariopasquato gotcha, based on the periodic table I thought you might have excluded it solely on safety, but the liquid and conductive natures make sense why it was ruled out. Are there any solid mercury compounds that are not conductive?
@EstMtz Sure there are https://en.m.wikipedia.org/wiki/Mercury(I)_chloride (still scores 3 on the health hazard scale)
Check out these markets for betting on the outcome of the experiment in case it is funded. Accurate probabilities may help estimate the expected scientific returns of the grant.
Will I find a violation? (amplified 100x)
If I find a violation will I come up with a theoretical explanation for it?